Not showing correctly on iPhone or iPad

Hi there!

I completed my wordpress website recently (see here: https://www.vlindermedia.nl) and have one small problem. When opened on an iPhone or iPad there’s a gap showing on the right. The header bar and the bars are not continued, they suddenly stop.

It works fine on a computer. Can someone give me a hint here? Hope you guys know what’s going on!

Thanks very much!
Kind regards,
Marlies